1. Field of the Invention
This invention relates to trucks for railroad vehicles and more particularly to a truck having a single wheelset.
2. Prior Art
Traditionally, a truck for use with a railroad vehicle has at least a pair of spaced wheelsets and is commonly referred to as "a 4-wheel truck". Each wheelset comprises two wheels joined to a free axle wherein the wheels and respective axle rotate as a unit. Such trucks were developed to support considerable loads and today are available with rated capacities of 100 tons or greater.
When the railroad vehicle is not required to carry such heavy loads, for example in passenger service or piggy-back type service of automotive trailers or containers, then the load carrying capacity of the truck may be reduced substantially.
One suggested railroad vehicle truck particularly adapted for lighter loads includes a single wheelset. The wheelset has its axle ends rotatively journaled in bearings. The bearings in turn operatively connect through an adapter to a centrally located pedestal jaw integrally formed as part of each of a pair of spaced longitudinally positioned side frames.
At each side frame end is an inwardly projecting bracket which in turn pivotally supports an upper end of a swing arm. Positioned laterally between the front and rear swing arm pairs is a crosstie assembly. Each assembly has a pair of end caps which pivotally connect respectively with a lower end of each swing arm pair.
Because the upper side frame bracket-swing arm pivot connections are located apart at a lesser distance than the lower crosstie assembly end cap-swing arm pivot connections, the crosstie assembly is self-leveling. Each crosstie assembly end cap has a pair of cups which contain lower ends of set of springs. Upper ends of the spring sets are operatively connected to a body of the railroad vehicle and resiliently support such.
The railroad truck as described above in theory provides certain advantages over the traditional 4-wheel truck. First, the mass of the truck is reduced. This lesser mass between the track and the car body reduces track wear and reduces the energy required to move the railroad vehicle body associated with the truck. This mass can be further minimized by using components having an optimum strength-to-weight ratio.
The railroad vehicle truck as described, however, has not been built and tested to prove its ability to operate satisfactorily in the harsh environment of railroading. To evaluate the structural integrity of the design prior to actual fabrication and field testing, the various components were studied using computerized finite element analysis. This analysis revealed that the initial design of the side frames and crosstie end caps could be expected to fail when subjected to static and dynamic forces which the truck would typically encounter during use.